1. Field of the Invention
The present invention relates to a Join message load control system and method in a network using a Protocol Independent Multicast-Source Specific Multicast (PIM-SSM), and more particularly, to a Join message load control system and method in a network using a PIM-SSM, which may be dynamically aware of whether a channel is active or inactive and may also reduce transmission of an unnecessary packet in a network.
2. Description of the Related Art
Recently, a great amount of broadcast traffic exists in networks all over the world. The same traffic may be transferred as a unicast to a plurality of receivers.
In a network using the unicast, when a data packet such as broadcast traffic must be transmitted to a plurality of receivers, same packet must be transmitted in duplicate. Therefore, the deterioration of the efficiency of the entire network may be caused.
Meanwhile, in such environments, a multicast clones the broadcast traffic and transfers the cloned broadcast traffic to the plurality of receivers. Therefore, it is possible to prevent duplicated unicast traffic from being unnecessarily transmitted and reduce consumption of network sources.
For example, in the case of a company broadcast that all the employees in the company need to view and listen to every day and at the same time, if the company broadcast is a unicast, broadcast traffic must be transmitted in duplicate to the respective personal computers (PCs) of the employees.
When the company broadcast is a multicast, however, a multicast server transmits the broadcast traffic only once and intermediate multicast routers clone the received broadcast traffic and transmit the cloned broadcast traffic to lower routers.
Examples of a scheme that uses the multicast include a Protocol Independent Multicast-Sparse Mode (PIM-SM) and a Protocol Independent Multicast-Source Specific Multicast (PIM-SSM).
In this instance, the Protocol Independent Multicast-Sparse Mode (PIM-SM) functions to transmit a multicast packet to a multicast group and effectively operate in a Wide Area Network (WAN) environment.
Irrespective of what type of unicast routing protocol is being used, such as Border Gateway Protocol (BGP), an Open Shortest Path First (OSPF) protocol, a Routing Information Protocol (RIP), and the like, the Protocol Independent Multicast-Sparse Mode (PIM-SM) uses existing unicast routing information and thus is referred to as “Protocol-Independent”.
On the other hand, a multicast protocol such as a distance vector multicast routing protocol constructs unicast routing information by itself.
Since the Protocol Independent Multicast-Sparse Mode (PIM-SM) is a protocol designed for multicast groups that exist in the extensive scope of regions, the Protocol Independent Multicast-Sparse Mode (PIM-SM) may be more effectively operated in the Wide Area Network (WAN) environment.
The Protocol Independent Multicast-Sparse Mode (PIM-SM) supports a shared-tree and a source-based tree, that is, a shortest-path tree.
When the Protocol Independent Multicast-Sparse Mode (PIM-SM) supports the shared-tree, a central router, that is, a rendezvous point (RP), is used as a root of the shared tree and a first hop router that is directly connected to a multicast source transmits a received multicast traffic to rendezvous point (RP). Last-Hop Routers are directly connected to multicast receivers. Next, rendezvous point (RP) transfers the multicast traffic to all of multicast receivers that are included in a corresponding multicast group through the shared-tree. For this operation, all of multicast receivers enroll at the Internet Protocol (IP) multicast group information that multicast receivers desires to receive. Therefore, traffic from multicast source comes down to Rendezvous point (RP) through First-Hop Router and Rendezvous point (RP) transmits the traffic to multicast receivers through Last-Hop Routers.
When the Protocol Independent Multicast-Sparse Mode (PIM-SM) supports the source-based tree, on the other hand, a source tree exists for each multicast source. A last-hop router that is connected to multicast receiver finds a shortest path heading toward a corresponding multicast source and multicast source joins a multicast group whereby the multicast traffic is transferred to each multicast receiver via the source tree.
The two schemes described above initially transfer the multicast traffic via the shared-tree and convert to the source tree at the last-hop router when the multicast traffic is transferred to the multicast receiver.
The Protocol Independent Multicast-Source Specific Multicast (PIM-SSM) always uses the source tree, instead of using the shared tree, based on the above-described Protocol Independent Multicast-Sparse Mode (PIM-SM). In the Protocol Independent Multicast-Sparse Mode (PIM-SM) scheme, multicast receivers are aware of information on the multicast source (i.e., the multicast server) and information on the multicast group that the multicast receiver desires to join. The multicast receiver operates in such a manner to join the multicast source and multicast group information at the router.
Also, with respect to a particular multicast source and a particular multicast group, the Protocol Independent Multicast-Source Specific Multicast (PIM-SSM) transfers the multicast traffic only to a joined multicast receiver. Specifically, when it is assumed that the multicast source that the receiver desires to join is ‘S’ and an address of the multicast group is ‘G’, the receiver joins (S, G), which is referred to as a channel(S, G).
The multicast traffic of the PIM-SSM is transferred only through the channel(S, G).
In order for the multicast receiver to join the channel(S, G), Internet Group Management Protocol Version 3 (IGMPv3) must be supported.
Instead of the Protocol Independent Multicast-Source Specific Multicast (PIM-SSM) initially transferring the multicast traffic through the shared-tree and subsequently converting to the source-based tree, multicast receivers are already aware of the multicast source and then joins the channel(S, G). Therefore, the concept of the shared tree is not needed. Accordingly, the Protocol Independent Multicast-Source Specific Multicast (PIM-SSM) uses only the source-based tree, that is, the shortest-path tree, without using the shared-tree and the Rendezvous point (RP).
When a multicast receiver joins a channel(S, G) and transmits a ‘Join’ message to a first router (i.e., a last-hop router) at the first step, and the last-hop router receives a ‘Join’ message from the multicast receiver and must periodically, for example, at a default time interval of 60 seconds, transmit a Protocol Independent Multicast-Sparse Mode (PIM-SM) Join message(S, G) to a second router (i.e., a first-hop router) heading toward multicast source S at the second. Next, the higher level router receives the Join message(S, G) from the lower level router (i.e., last-hop router) and also periodically transmits the Join message(S, G) to a third router, that is, another higher router heading toward the multicast source S at the third step.
When using the Protocol Independent Multicast-Source Specific Multicast (PIM-SSM), different applications may use different multicast source addresses for multicast group addresses, respectively.
On the other hand, when using the Protocol Independent Multicast-Sparse Mode (PIM-SM), different applications use the same multicast group address. Therefore, the applications may receive undesired multicast traffic.
When a multicast receiver joins a channel(S, G) and transmits a ‘Join’ message to a first router (i.e., a last-hop router), and the last-hop router receives a ‘Join’ message from the multicast receiver and must periodically, for example, at a default time interval of 60 seconds, transmit a Protocol Independent Multicast-Sparse Mode (PIM-SM) Join message(S, G) to a second router (i.e., a higher level router) heading toward a multicast source S.
Next, the higher level router receives the Join message(S, G) from the lower level router (i.e., last hop router) and also periodically transmits the Join message(S, G) to a third router, that is, another higher router heading toward the multicast source S.
Through the above process of joining the channel(S, G), the first, the second, and the third routers in the network may create and maintain the channel(S, G).
In this instance, the third router that is a first-router heading toward the multicast source may receive the multicast traffic from the multicast source S and immediately transfer the multicast traffic to a lower router through the created channel(S, G).
When the third router receives the multicast traffic(S, G) from the multicast source S, the third router starts a Keep-Alive Time (KAT) timer. The KAT timer is used to delete the channel(S, G) when the multicast traffic(S, G) is initially received from the multicast source S and another multicast traffic(S, G) is not received from the multicast source S during a predetermined period of time.
Even though the multicast traffic(S, G) is not received from the multicast source S, when a (S, G) Protocol Independent Multicast (PIM) Join message is received from a lower hop router, the KAT timer does not delete the channel(S, G). Only when the (S, G) Protocol Independent Multicast (PIM) Join message is not received from the lower hop router, the KAT timer is used to delete the corresponding channel(S, G).
The contemporary Protocol Independent Multicast-Source Specific Multicast (PIM-SSM), however, does not have a function for informing the multicast receiver side about whether a multicast source is active or inactive. Therefore, a multicast receiver cannot be aware of whether the multicast source is active or inactive.
Accordingly, even though the channel(S, G) is not active anymore, that is, even though the multicast source S does not transmit the multicast traffic to the multicast group G for a long time period, or even though the multicast source S does not transmit the multicast traffic to the multicast group G anymore, in a state where the multicast receiver joins the channel(S, G), the last-hop router must periodically, for example, once every 60 seconds, transmit a Join message(S, G) to a higher hop router. Also, a router connected to the multicast source and all of the intermediate routers must periodically transmit Join messages(S, G) which requires transmission of an unnecessary packet be transmitted, and thereby causes a heavy traffic load in a network. Therefore, it is preferable that in a heavily loaded wireless communication system, any unnecessary packet transmission is either eliminated or reduced. Transmission of ‘Join’ messages for routers joining desired channels and for multicast receivers joining desired channels is one part of the entire packet of a transmission in the wireless communication system. Moreover, any unnecessary packet load should be reduced as much as possible in any communication system. Therefore, either eliminating or reducing the transmissions of ‘Join’ messages is one desirable way to prevent an unnecessary traffic load from being added to the wireless communication system, and for thus improving the efficiency of the communication system.